1. Technical Field
The present invention relates to an electroluminescent light-emitting device and an electronic apparatus including the same, and a film-forming method suitably applied to the manufacturing processes of the device and apparatus.
2. Related Art
Among lightweight, thin light-emitting sources is an OLED (organic light emitting diode), that is, organic EL (electro luminescent) element. The organic EL element has a structure including at least one organic thin layer made of an organic material disposed between a pixel electrode and an opposing electrode. In this structure, the pixel electrode may act as an anode and the opposing electrode may act as a cathode. As a current is applied between these electrodes, the current flows through the organic thin layer, and thereby the organic thin layer, or the organic EL element, emits light. In this instance, the emission intensity depends on the magnitude of the current flowing through the organic thin layer. It is therefore necessary to pay due attention to control of the current, or potentials of the pixel electrode and the opposing electrode.
By arranging a large number of such organic EL elements and by appropriately controlling emission/non-emission of each organic EL element, images or the like representing a desired meaning can be displayed.
For example, Japanese Unexamined Patent Application Publication No. 2001-284041 discloses such an organic EL element and an image display apparatus including the organic EL elements.
The image display apparatus disclosed in this patent document has a known problem with current control and, in addition, a disadvantage in lifetime of the organic EL element. More specifically, the organic thin layer cannot emit light forever, of course, and it reaches the end of its lifetime after being used over a long term.
While such natural degradation is one of the problems with the lifetime of organic EL elements, the most critical problem is that some factors reduce the lifetime. A representative example of the factors is the presence of moisture and oxygen in the atmosphere. Undesirably, moisture and oxygen penetrate the organic thin layer to reduce the electroconductivity of the organic thin layer, or to degrade the adhesion between the organic thin layer and the electrodes.
In order to prevent these problems, thin film sealing is generally applied. In this technique, a ceramic thin layer superior in blocking oxygen and moisture is formed of, for example, silicon nitride to cover the organic EL element, thereby preventing oxygen and moisture from penetrating into the organic EL element.
However, the technique of thin film sealing has the following disadvantages. The ceramic sealing film is liable to crack because it is generally made of a relatively hard material, such as silicon nitride or silicon oxynitride. Once a crack occurs in the sealing film, moisture or oxygen comes into the organic EL element through the crack. Thus, the sealing film cannot function as intended.
The above-cited patent document discloses an application of the thin film sealing technique. In the patent document, an “inorganic passivation layer” is characterized as a layer having the function of blocking moisture (Paragraph [0017]). For reference sake, the cited patent document essentially discloses the following techniques (items inside parentheses refer to claim numbers or paragraph numbers in the patent document):
(i) Sealing films covering both sides of a partition member and protruding from a substrate (Claim 1) are formed between organic EL elements. (ii) The inorganic passivation layer is formed to cover the sealing films (Claim 1, and paragraphs [0015] and [0016]). (iii) Thus, the resulting inorganic passivation layer does not have steep slopes at both sides of the partition member, but easy slopes or smooth surfaces (paragraph [0021]). (iv) Although it is considered that the sides of the partition member, or the reverse-tapered portions at the sides of the partition member, easily transmit moisture and oxygen (paragraph [0021]), the inorganic passivation layer more appropriately block the moisture and oxygen because of the above (iii).
Although the cited document mentions “cracks” in, for example, paragraph [0016], it is not clearly shown whether the technique of the cited document is provided from the viewpoint described above.
In addition, the presence of the sealing film, which underlies the inorganic passivation layer, allows the inorganic passivation layer to be smooth in the cited document (see (ii) above). More specifically, the cited document focuses its feature on covering the reverse-tapered portions (FIG. 1 in the cited document) with the sealing film (FIG. 4 and paragraph [0022] in the cited document). Accordingly, the goal of the invention of the cited document is as described in (iv) above.
Therefore, the technique disclosed in the cited document may not sufficiently solve the above-described problems. To cover the reverse-tapered portions with the sealing film (or to cover the sides of the partition member with the sealing films, as stated in Claim 1) does not theoretically solve the problems.
Furthermore, the technique of the cited document essentially requires forming the sealing film as stated in Claim 1 of the cited document and as described above. This requires additional manufacturing steps and accordingly increases cost. From the viewpoint of achieving thin film sealing, however, only an inorganic passivation layer is essential.